When You do play story campaign on easy mode....
Some missions have one or two or three or four way battle depending on what missions is.....
You have ask yourself questions as such like this
IF They bring Tanks........I will say Attack them with Bomber as it make my life easier
IF they bring Aircraft then Bring Ground Guns to shoot the airplane down as they can hide in Forest
IF They bring Armys then they can go in Forest and can shoot anythings what throw them but if the tank can shoot in the forest then Armys going have problem
IF they bring Rocket gun that have long range then I need bring tanks to hunt them down quickly as possible otherwise it can kill my Base!
IF they bring Nuke then I have to do somethings really quickly like bring British bomber aircraft to kill them quickly as possible otherwise it is good nite for me! The Nuke have long range and if it does land your base.....then It will be very hard you to fight back!
The hardest level out of all is the Mission 22 and Mission 23(Very Tough depending on SKILL Level!) as it like 4 way battle but at the same time.....you are controling two Different Battlefield which is Tough Task as if you fail on one Battlefield then the Missions is Over!
Here all the Armys for to have good read about http://ruse.wikia.com/wiki/Factions